70 research outputs found
Edaq530: a transparent, open-end and open-source measurement solution in natural science education
We present Edaq530, a low-cost, compact and easy-to-use digital measurement
solution consisting of a thumb-sized USB-to-sensor interface and a measurement
software. The solution is fully open-source, our aim being to provide a viable
alternative to professional solutions. Our main focus in designing Edaq530 has
been versatility and transparency. In this paper, we shall introduce the
capabilities of Edaq530, complement it by showing a few sample experiments, and
discuss the feedback we have received in the course of a teacher training
workshop in which the participants received personal copies of Edaq530 and
later made reports on how they could utilise Edaq530 in their teaching
Tuning the Correlation Decay in the Resistance Fluctuations of Multi-Species Networks
A new network model is proposed to describe the resistance noise
in disordered materials for a wide range of values ().
More precisely, we have considered the resistance fluctuations of a thin
resistor with granular structure in different stationary states: from nearly
equilibrium up to far from equilibrium conditions. This system has been
modelled as a network made by different species of resistors, distinguished by
their resistances, temperature coefficients and by the energies associated with
thermally activated processes of breaking and recovery. The correlation
behavior of the resistance fluctuations is analyzed as a function of the
temperature and applied current, in both the frequency and time domains. For
the noise frequency exponent, the model provides at low
currents, in the Ohmic regime, with decreasing inversely with the
temperature, and at high currents, in the non-Ohmic regime.
Since the threshold current associated with the onset of nonlinearity also
depends on the temperature, the proposed model qualitatively accounts for the
complicate behavior of versus temperature and current observed in many
experiments. Correspondingly, in the time domain, the auto-correlation function
of the resistance fluctuations displays a variety of behaviors which are tuned
by the external conditions.Comment: 26 pages, 16 figures, Submitted to JSTAT - Special issue SigmaPhi200
Gain in Stochastic Resonance: Precise Numerics versus Linear Response Theory beyond the Two-Mode Approximation
In the context of the phenomenon of Stochastic Resonance (SR) we study the
correlation function, the signal-to-noise ratio (SNR) and the ratio of output
over input SNR, i.e. the gain, which is associated to the nonlinear response of
a bistable system driven by time-periodic forces and white Gaussian noise.
These quantifiers for SR are evaluated using the techniques of Linear Response
Theory (LRT) beyond the usually employed two-mode approximation scheme. We
analytically demonstrate within such an extended LRT description that the gain
can indeed not exceed unity. We implement an efficient algorithm, based on work
by Greenside and Helfand (detailed in the Appendix), to integrate the driven
Langevin equation over a wide range of parameter values. The predictions of LRT
are carefully tested against the results obtained from numerical solutions of
the corresponding Langevin equation over a wide range of parameter values. We
further present an accurate procedure to evaluate the distinct contributions of
the coherent and incoherent parts of the correlation function to the SNR and
the gain. As a main result we show for subthreshold driving that both, the
correlation function and the SNR can deviate substantially from the predictions
of LRT and yet, the gain can be either larger or smaller than unity. In
particular, we find that the gain can exceed unity in the strongly nonlinear
regime which is characterized by weak noise and very slow multifrequency
subthreshold input signals with a small duty cycle. This latter result is in
agreement with recent analogue simulation results by Gingl et al. in Refs. [18,
19].Comment: 22 pages, 5 eps figures, submitted to PR
Stochastic Resonance in Nonpotential Systems
We propose a method to analytically show the possibility for the appearance
of a maximum in the signal-to-noise ratio in nonpotential systems. We apply our
results to the FitzHugh-Nagumo model under a periodic external forcing, showing
that the model exhibits stochastic resonance. The procedure that we follow is
based on the reduction to a one-dimensional dynamics in the adiabatic limit,
and in the topology of the phase space of the systems under study. Its
application to other nonpotential systems is also discussed.Comment: Submitted to Phys. Rev.
Noise suppression by noise
We have analyzed the interplay between an externally added noise and the
intrinsic noise of systems that relax fast towards a stationary state, and
found that increasing the intensity of the external noise can reduce the total
noise of the system. We have established a general criterion for the appearance
of this phenomenon and discussed two examples in detail.Comment: 4 pages, 4 figure
Stochastic Resonance in Noisy Non-Dynamical Systems
We have analyzed the effects of the addition of external noise to
non-dynamical systems displaying intrinsic noise, and established general
conditions under which stochastic resonance appears. The criterion we have
found may be applied to a wide class of non-dynamical systems, covering
situations of different nature. Some particular examples are discussed in
detail.Comment: 4 pages, RevTex, 3 PostScript figures available upon reques
Nonstationary Stochastic Resonance in a Single Neuron-Like System
Stochastic resonance holds much promise for the detection of weak signals in
the presence of relatively loud noise. Following the discovery of nondynamical
and of aperiodic stochastic resonance, it was recently shown that the
phenomenon can manifest itself even in the presence of nonstationary signals.
This was found in a composite system of differentiated trigger mechanisms
mounted in parallel, which suggests that it could be realized in some
elementary neural networks or nonlinear electronic circuits. Here, we find that
even an individual trigger system may be able to detect weak nonstationary
signals using stochastic resonance. The very simple modification to the trigger
mechanism that makes this possible is reminiscent of some aspects of actual
neuron physics. Stochastic resonance may thus become relevant to more types of
biological or electronic systems injected with an ever broader class of
realistic signals.Comment: Plain Latex, 7 figure
Stochastic Resonance in a Dipole
We show that the dipole, a system usually proposed to model relaxation
phenomena, exhibits a maximum in the signal-to-noise ratio at a non-zero noise
level, thus indicating the appearance of stochastic resonance. The phenomenon
occurs in two different situations, i.e. when the minimum of the potential of
the dipole remains fixed in time and when it switches periodically between two
equilibrium points. We have also found that the signal-to-noise ratio has a
maximum for a certain value of the amplitude of the oscillating field.Comment: 4 pages, RevTex, 6 PostScript figures available upon request; to
appear in Phys. Rev.
Noise and Periodic Modulations in Neural Excitable Media
We have analyzed the interplay between noise and periodic modulations in a
mean field model of a neural excitable medium. To this purpose, we have
considered two types of modulations; namely, variations of the resistance and
oscillations of the threshold. In both cases, stochastic resonance is present,
irrespective of if the system is monostable or bistable.Comment: 13 pages, RevTex, 5 PostScript figure
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